Amazon Dash buttons are now essentially Free for a limited time

A month ago, Amazon ended their Dash Button invite-only program and made the devices available to all Prime members to buy for $4.99 each. They’ve now started a new promotion that essentially make the Dash Buttons free. If you buy a button for $4.99, Amazon will automatically take $4.99 off the first order you place by pressing that button. The promotion’s terms say you will receive “one promotional credit per Dash Button purchased”, so it’s $4.99 off for each button. Not just $4.99 off once per customer. With each button costing $4.99, that essentially makes the button free as long as you use it once.

With the addition of brands like Hefty, Dixie, Mrs. Meyer’s, and Ice Breakers Gum, Amazon has also increased the number of Dash Button brands available from 18 to 29. Each button can be configured to order one of 500 different products sold by Amazon. You connect the buttons via wifi and configure them with Amazon’s smartphone app to order a single product when the button is pressed. In order to prevent duplicate orders, additional presses will not order additional items until your order arrives from the first press.

The article is wrong. You say it takes the $4.99 off the first order, but actually, you pay $4.99 for the button and it give you $4.99 credit for the first time you use it. So you still have to pay the $4.99 up front to get the dash button.

Info is from the Promotional link you provided.

To receive the $4.99 promotional credit, you must make your first qualifying purchase through Dash Button by August 31, 2016.
Once applied to your account, the $4.99 promotional credit will be allocated proportionally among all qualifying items in your order(s).